Dual bridge angular and linear accelerometer

ABSTRACT

An accelerometer includes an inertial platform maintaining an attitude in response to a platform stabilizing controller signal and defining a spin axis and a reference plane. An accelerometer, coupled to the inertial platform a distance from the spin axis, defines a flex axis. The accelerometer generates an accelerometer signal in response to acceleration of the accelerometer. A second accelerometer defines a second flex axis, and is also coupled to the inertial platform a distance from the spin axis. The second accelerometer generates a second accelerometer signal in response to acceleration of the second accelerometer. A controller receives the first accelerometer signal and the second accelerometer signal and generates a linear acceleration signal in response to a sum of the first accelerometer signal and the second accelerometer signal and generates an angular acceleration signal from the difference. The controller further generates the platform stabilizing controller signal in response to the first acceleration signal and the second acceleration signal.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is related to application (Attorney Docket03-0169) entitled “Dual Bridge Angular Accelerometer,”filed on ______,Ser. No. ______ and incorporated by reference herein.

BACKGROUND OF INVENTION

The present invention relates generally to accelerometers, and moreparticularly, to a variable capacitance accelerometer generating angularand linear signals.

It is well known that capacitive accelerometers measure theacceleration, vibration and the inclination of objects to which they areattached. These objects typically include missiles, spacecraft,airplanes and automobiles.

In general, capacitive accelerometers change electrical capacitance inresponse to acceleration forces and vary the output of an energizedcircuit. Capacitive accelerometer systems generally include sensingelements, including capacitors, oscillators, and detection circuits.

The sensing elements include at least two parallel plate capacitorsfunctioning in differential modes. The parallel plate capacitorsgenerally operate in sensing circuits and alter the peak voltagegenerated by oscillators when the attached object undergoesacceleration.

When subject to a fixed or constant acceleration, the capacitance valueis also a constant, resulting in a measurement signal proportional touniform acceleration.

This type of accelerometer can be used in an aerospace or in a portionof aircraft or spacecraft navigation or guidance systems. Accordingly,the temperature in the operating environment of the accelerometerchanges over a wide range. Consequently, acceleration must be measuredwith a high accuracy over a wide range of temperatures and temperaturegradients. This is often a difficult and inefficient process.

Additionally, missile systems require a high degree of accuracyregarding angular and linear acceleration measurements. Improvements inthis regard are constantly being sought out.

The disadvantages associated with current accelerometer systems havemade it apparent that a new accelerometer is needed. The newaccelerometer should substantially minimize temperature sensingrequirements and should also improve acceleration detection accuracy.The present invention is directed to these ends.

SUMMARY OF INVENTION

In accordance with one aspect of the present invention, an accelerometerincludes an inertial platform defining a z spin axis, an xz referenceplane, and a y linear acceleration axis. The inertial platform maintainsan attitude in response to a platform stabilizing controller signal. Afirst accelerometer defines a first flex axis and is coupled to theinertial platform a first distance from the spin axis. The firstaccelerometer generates a first accelerometer signal in response toacceleration of the first accelerometer. A second accelerometer definesa second flex axis and is coupled to the inertial platform a seconddistance from the spin axis. The second accelerometer generates a secondaccelerometer signal in response to acceleration of the secondaccelerometer. A controller receives the first accelerometer signal andthe second accelerometer signal and generates a linear accelerationsignal in response to a sum of the first accelerometer signal and thesecond accelerometer signal. The controller further generates theplatform stabilizing controller signal in response to the firstacceleration signal and the second acceleration signal.

In accordance with another aspect of the present invention, a method foroperating a dual bridge accelerometer system defining a z spin axisincludes generating a first accelerometer signal from a first bridgeaccelerometer and generating a second accelerometer signal from a secondbridge accelerometer. The first bridge accelerometer and the secondaccelerometer are controlled such that they remain in the xz-plane. Afirst output word is generated from the first bridge accelerometerequivalent to a sum of a first linear acceleration and a firsttangential acceleration acting on the first bridge accelerometer. Asecond output word is generated from the second bridge accelerometerequivalent to a sum of the first linear acceleration and the firsttangential acceleration acting on the second bridge accelerometer. Thefirst output word is averaged with the second output word, and a linearacceleration signal is generated.

One advantage of the present invention is that it generates a dynamicrange and granularity sufficient for Inter-Continental Ballistic Missile(ICBM) usage. Moreover, the bridge accelerometer consumes less powerthan current accelerometers, while dramatically improving reliability.

The dual bridge angular and linear accelerometer, or dual bridgeaccelerometer, generates reliable angular and linear accelerationmeasurements. These measurements are accurate to the degree required bymissile systems and will therefore provide a dramatic improvement inreliability and manufacturing costs.

Another advantage is that it is not substantially affected by changes intemperature or temperature gradients. The bridge configuration reducesthe temperature sensitivity, thereby enhancing the signal-to-noiseratio.

Additional advantages and features of the present invention will becomeapparent from the description that follows, and may be realized by meansof the instrumentalities and combinations particularly pointed out inthe appended claims, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

In order that the invention may be well understood, there will now bedescribed some embodiments thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 illustrates an aerospace system including an angular and linearaccelerometer system in accordance with one embodiment of the presentinvention;

FIG. 2 illustrates a pictorial diagram of the angular and linearaccelerometer system in accordance with FIG. 1;

FIG. 3 illustrates a side view (x-y view) of FIG. 2;

FIG. 4 illustrates a logic diagram of an angular and linearaccelerometer in accordance with another embodiment of the presentinvention;

FIG. 5 illustrates an accelerometer from the angular and linearaccelerometer system of FIG. 1;

FIG. 6 illustrates the equivalent circuit for the capacitors of FIG. 5;and

FIG. 7 illustrates a logic flow diagram of the aerospace system of FIG.1 in operation, in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION

The present invention is illustrated with respect to an angular andlinear accelerometer, particularly suited to the aerospace field. Thepresent invention is, however, applicable to various other uses that mayrequire accelerometers, such as any system requiring position andvelocity measurements under extreme conditions, as will be understood byone skilled in the art.

Referring to FIG. 1, the system 10, which is an aerospace, accelerometersystem, including an angular and linear accelerometer system 12 withinan inertial measurement unit 13, is illustrated. The aerospace system 10is merely an illustrative example of an accelerating object and notmeant to be limiting. For example, the present angular and linearaccelerometer 12 could be implemented in any accelerating object tosense acceleration forces, including any type of vehicle or missilesystem, such as a Minuteman III missile system or a Scud missile system.

The illustrated aerospace system 10 includes an inertial measurementunit 13 including at least one angular and linear accelerometer 12 and aserial data bus 18. The system 10 further includes gimbal and torquemotors 20, a computer/processor 14 (controller), and missile steeringnozzle or vane actuators 16.

The angular and linear accelerometer 12 is coupled to the gimbals andgimbal torque motors 20 (yaw, pitch and roll motors). The accelerometer12 is also coupled to the serial bus 18, which transfers information tothe computer/processor 14. For multiple angular and linearaccelerometers, the serial data bus 18 receives the accelerometersignals and sends them serially to the processor 14. The computer 14 iscoupled to the missile steering nozzle (or vane actuators) unit 16 andthe gimbal torque motors 20.

Referring to FIGS. 2 and 3, the angular and linear accelerometer 12 isillustrated. Two bridge accelerometers 15, 17, configured per FIGS. 4and 5, are included to implement the angular and linear accelerometer12.

The first bridge accelerometer 15 is positioned a distance r₁ fromthecentral y-axis (linear acceleration axis) or the z spin axis, and thesecond bridge accelerometer 17 is positioned a distance r₂, from thecentral y-axis or the z spin axis. Both bridge accelerometers 15, 17 arerepresented as plates having axes along the flex axes of the bridgeaccelerometers 15, 17.

One embodiment of the present invention includes the faces of the platesin the xz-plane, perpendicular to the y-axis at distances r₁ and r₂ fromthe coordinate origin. Numerous other arrangements are also includedherein, such as the faces of the plates in the yz or xz planes foralternate configurations.

For the present invention, r₁=r₂. This is merely one embodiment, and infact, they may be both on either side of the origin, as long as they areseparated by a known distance, and at a known distance from the origin.

The first and second bridge accelerometers 15, 17 are herein included onan inertial platform. The platform may be a gimbal 20 or alternateinertial platform design known in the art. The system 10 utilizes thegenerated signals from the accelerometers 15, 17 to control the platformposition to maintain a near zero rotation.

Referring to FIG. 4, a block diagram 100 of signal generation logic,within the computer 14 for the linear and angular acceleration system10, is illustrated.

In block 102, the distance, d of the flexured plates to the fixedplates, is proportional to the acceleration variable (as in the equationF=ma), which determines the bridge output voltage. As each accelerometersenses acceleration, either linear or angular-tangential, they deflectthe sum of the forces. Because the computer/processor 14 maintains theflexure plates in the xz-plane, the total acceleration acting on eachbridge accelerometer 15, 17 is the sum of the linear acceleration andthe tangential acceleration or linearized digital output. This isillustrated in block 102 as (a+α) for the first bridge accelerometer 15and (a−α) in block 104 for the second bridge accelerometer 17. In otherwords, there are generated output words for the first bridgeaccelerometer 15 of φ₁=(a+α)k and for the second bridge accelerometer 17of φ₂=(a−α)k.

In block 106, for equal distances of r and r₂, φ₁=k₁a+k₂ α and φ₂=k₃ak₄α, and k₁ and k₃ are equal if r₁=r₂. Otherwise they may be calculatedor modeled for the exact expression. In this simplified case,φ₁−φ₂=(k₂α)−(−k₄α) and therefore α=k (φ₁−φ₂)/2, where k is a constant tobe determined at manufacture, e.g. k may be defined to depend onmaterials and size constraints. αis then scaled and compensated in thecompensator block 110.

In block 108, the angular and linear accelerometer outputs are alsoadded to eliminate αin a similar manner. The output then becomesa=k(φ₁+φ₂)/2 in block 108. It is then also scaled and compensated in thecompensator block 112 to generate a digital word proportional to linearacceleration.

The circuitry illustrated in FIG. 4 applies the sum and differenceamplitudes from blocks 106 and 108 to a compensation circuit in thecompensator blocks 110 and 112, which may be lookup tables, forproviding compensation for the non-linearities induced by the particularmechanical misalignment, manufacturing and other data path anomalies.

One output (α) is a digital word proportional to the rotational(angular) acceleration in either direction about the z-axis. The otheroutput (a) is a digital word proportional to the linear acceleration ineither direction in the y-axis.

Referring to FIGS. 5 and 6, a bridge accelerometer in accordance withFIGS. 1, 2 and 3 is illustrated. Each bridge accelerometer 15 orvariable capacitance bridge accelerometer (VCBA) within the angular andlinear accelerometer 12 is a single axis accelerometer that generates arobust wide dynamic range of performance. Important to note is thatalternate embodiments of the present invention have one or moreaccelerometers, the two illustrated accelerometers 15, 17 are only oneexample of a possible arrangement of accelerometers, and any number ofaccelerometers can be utilized.

The accelerometer 15 will be described as an illustrative example of thetwo accelerometers 15, 17 in this embodiment. The accelerometer 15 ispart of the inertial measurement unit 13 and includes a housing 36, aflexured plate section 22, a rigid plate section 24, a ground 38, an ACsource 40, a differential amplifier 42, a demodulator 44, an analogfilter 46, an analog-to-digital converter 48, and a digital linearizerand filter 50.

The housing 36 or metal housing structure encloses four capacitors,which will be discussed later. A gas or vacuum environment is alsoenclosed therein such that there is no interference with the movement ofthe flexure plate 30 other than the acceleration of the system 10 alonga perpendicular axis.

The flexured plate section 22 includes a single flexure plate 30 and twoparallel fixed plates 32, 34. The rigid plate section 24 includes arigid plate and two fixed plates. The two sections are electricallyisolated and enclosed in a metal housing structure 36.

In the present embodiment, the flexure plate 30 is coupled to thehousing 36 at only one edge 37. Numerous other attachment points are,however, included, as will be understood by one skilled in the art. Theflexure plate includes a first side 31, a second side 33 and a commonedge 37.

The flexure plate 30 is positioned between the first and second fixedplates 32, 34 such that the first fixed plate 32 is a first distance(d₁) from the first side 31 and the second fixed plate 34 is a seconddistance (d₂) from the second side 33 of the flexure plate 30. Theflexure plate 30 is affixed to the metal housing structure 36 through atleast a portion of the common edge 37 of the flexure plate 30, which isalso coupled to a ground 38.

The flexure plate is rigidly fixed to the metal housing structure 36through almost any manner known in the art. Resultantly, all the systemflexure is generated within the flexure plate 30 along a flex axis (forthe first accelerometer 15 this is a first flex axis, for the secondaccelerometer 17, this is the second flex axis). This generallyincreases reliability and robustness of the system 10. This, however,generates a non-linear output from the flexure plate 30, which will bediscussed regarding the linearizer 50.

The combination of the first fixed plate 32 and the flexure plate 30forms a first parallel plate capacitor, and the combination of thesecond fixed plate 34 and the flexure plate 30 forms the second parallelplate capacitor. The equivalent capacitor for the first parallel platecapacitor is illustrated in FIG. 6 in broken lines as C₁, and theequivalent capacitor for the second parallel plate capacitor isillustrated in broken lines as C₂.

The capacitance of the parallel plate capacitors is determined by thefollowing:C≅(ε₀A)/d,where

-   ε₀    is the permittivity constant, A is the area of a fixed plate 32 or    34, and d is the effective distance between the flexure plate 30 and    one of the fixed plates 32, 34.

The first fixed plate 32 is coupled to the metal housing structure 36and positioned a first distance (d₁) from the flexure plate 30. Thefirst fixed plate 32 and the flexure plate 30 form a first capacitorwhose operation is also governed by the equationC≅(ε₀A)/d

The first fixed plate 32 responds to movement of the flexure plate 30when d₁ either increases or decreases, thereby generating a first phaseshift capacitance signal.

The second fixed plate 34 is also coupled to the metal housing structure36 and positioned a second distance (d₂) from the flexure plate 30. Thesecond fixed plate 34 and the flexure plate 30 form a second capacitorwhose operation is governed by the equationC≅(ε₀A)/d.

The second fixed plate 34 responds to movement of the flexure plate 30when d₂ either increases or decreases, thereby generating a second phaseshift capacitance signal.

The distances (d₁ and d₂) between the flexure plate 30 and the fixedplates 32, 34 are a function of acceleration and are proportional orequal when the system 10 is at rest.

During acceleration, the flexure plate 30 flexes according to thereaction force of Newton's second law of motion, force=mass×acceleration(F=ma), causing the distance between the flexure plate 30 and the fixedplates 32, 34 to vary, thus creating the two variable capacitors C₁, C₂,one on each side of the flexure plate 30.

For the rigid plate section 24, which is insulated from the flexuredplate section 22, the rigid plate 60 is positioned between the thirdfixed plate 62 and fourth fixed plate 64 such that the third fixed plate62 is a third distance (d₃) from a first side 66 and the fourth fixedplate 64 is a fourth distance (d₄) from a second side 68 of the rigidplate 60. The rigid plate 60 is coupled to an insulator 70 through atleast a portion of at least one common edge 72 of the first side 66 andthe second side 68 of the rigid plate 60, and the insulator 70 isaffixed to the metal housing structure 36. The third and fourth fixedplates 62, 64 are coupled to the housing 36.

In the present embodiment, the rigid plate 60 is coupled to the housing36 through an insulator at only one edge 72. However, numerous otherattachment points are included, as will be understood by one skilled inthe art.

The combination of the third fixed plate 62 and the rigid plate 60 formsa third parallel plate capacitor, and the combination of the fourthfixed plate 64 and the rigid plate 60 forms the fourth parallel platecapacitor. The equivalent capacitor for the third parallel platecapacitor is illustrated in broken lines in FIG. 6 as C₃, and theequivalent capacitor for the forth parallel plate capacitor isillustrated in broken lines as C₄.

The first and second capacitors are formed on each side of the flexureplate 30 and the third and fourth capacitors are formed on either sideof the rigid plate 60. The four capacitors are electrically connected toform a bridge. The fixed capacitors (third and fourth) and rigid plate60 are isolated from the flexured plate 30 and flexured plate capacitors(first and second). All capacitors are designed to be as nearly equal aspossible when at rest.

The distance between the flexure plate 30 and the rigid plate 60 is afunction of acceleration. The center of each bridge side (ED and BF inFIGS. 5 and 6) is monitored to detect the differential amplitude. As theflexure plate 30 flexes in response to acceleration, one capacitorincreases and the other decreases, thereby increasing the bridge voltageon one side and decreasing bridge voltage on the other.

The bridge is excited with an AC source 40 at one end (A) and groundedat the other end (C). The ground 38 is coupled to the flexure plate 30and the AC source 40 is coupled to the rigid plate 60. The twocapacitive legs (ADEC) and (ABFC) of the bridge produce two voltagedividers, each of which provides a terminal (ED, BF), illustrated inFIG. 6, to measure the resulting voltage.

The bridge configuration reduces the temperature sensitivity and the ACexcitation allowing narrow band analog filtering, both of which enhancethe signal-to-noise ratio. The bridge circuitry utilizes GaAs or highspeed CMOS, as the accuracy required for performance will require lowpropagation delays. In one embodiment, the bridge circuitry is mountedon a heated housing structure. In addition, the entire system includes aprecision heating device (not shown) and sufficient mass to reducegradients in the bridge in one embodiment.

The voltage phase gives direct indication of the direction ofacceleration. This output is gain adjusted if required in thedifferential amplifier 42, and received in the demodulator 44, whichrectifies the waveform as a function of the reference excitation phasefrom the AC source 40. The resulting waveform is then filtered in theanalog domain in the analog filter 46 and received in ananalog-to-digital converter 48 where the data becomes a digital word.

The digital word is then filtered and linearized in the digitallinearizer and filter 50 for manufacturing and flexure non-uniformities.This output is a digital word having a magnitude proportional to theacceleration of the system in either direction along the perpendicularaxis.

In other words, the linearizer 50 receives the overall digital wordsignal. The linearizer 50 compensates for both the nonlinear functiongenerated from the analogto-digital converter 48 and any manufacturinganomalies, as will be understood by one skilled in the art. Thelinearizer 50 value is established in manufacturing through taking largesamples of performance curves, as will be understood by one skilled inthe art. The linearizer 50 output is a digital word whose magnitude isproportional to the acceleration of the system 10 in either directionalong an axis perpendicular to the flexure plate 30.

Numerous alternate linearizers are also included in the presentembodiment whereby a substantially linear function can be generated bycompensating for nonlinear functions, for example, in the digitaldomain, a digital linearizer is included. The output of the linearizer50 is an acceleration signal multiplied by a constant (k).

Statistical filtering of the linearized data somewhere significantlyabove the maximum flexure frequency also occurs in either the digitallinearizer and filter 50 or the computer 14 to reduce the overall noiseimpact on the system 10. The compensation for the non-linearity of theflexure structure and overall transport error is compensated for by thelinearizer and filter 50 whose values are established in manufacturingthrough sampling performance curves.

The computer 14 receives the acceleration signal multiplied by theconstant and generates a computer signal and response thereto. Thecomputer 14 is embodied as a typical missile or airplane computer, as isfamiliar in the art.

The missile steering nozzle or vane actuators 16 receive the computersignal and activate the gimbal torque motors 20 or object controldevices in response thereto.

A functional angular accelerometer consists of a pair of DifferentialBridge Accelerometers (DBA), each of which is configured as shown inFIG. 5. Each DBA is a single axis accelerometer that can provide areliable wide dynamic range of performance.

Referring to FIG. 7, a logic flow diagram 120 illustrating a method forgenerating angular and linear acceleration signals is illustrated. Logicstarts in operation block 122 where the platform is moved or acceleratedand the two accelerometers 15, 17 generate accelerometer signals i.e.linearized digital output signals.

In operation block 124, the computer 14 maintains the accelerometers 15,17 in the xz-plane either in response to the accelerometer signals orthe angular and linear signals generated by the system 10.

In operation block 128, the total of first accelerometer signal minusthe second accelerometer signal is divided in half to generate theangular acceleration output word.

In operation block 130, the total of the first accelerometer signal plusthe second accelerometer signal is divided in half to generate thelinear acceleration output word.

In operation block 132, the angular acceleration word and the linearacceleration word are compensated in the compensators 106, 108.

In operation, a method for operating a dual bridge accelerometer systemdefining a z spin axis includes generating a first accelerometer signalfrom a first bridge accelerometer and generating a second accelerometersignal from a second bridge accelerometer. The first bridgeaccelerometer and the second accelerometer are controlled such that theyremain in the xz-plane. A first output word is generated from the firstbridge accelerometer equivalent to a sum of a first linear accelerationand a first tangential acceleration acting on the first bridgeaccelerometer. A second output word is generated from the second bridgeaccelerometer equivalent to a sum of the first linear acceleration andthe first tangential acceleration acting on the second bridgeaccelerometer. The first output word is averaged with the second outputword, and a linear acceleration signal is generated.

From the foregoing, it can be seen that there has been brought to theart a new and improved accelerometer system. It is to be understood thatthe preceding description of the preferred embodiment is merelyillustrative of some of the many specific embodiments that representapplications of the principles of the present invention. For example, avehicle, such as an airplane, spacecraft, or automobile could includethe present invention for acceleration detection and control. Numerousand other arrangements would be evident to those skilled in the artwithout departing from the scope of the invention as defined by thefollowing claims.

1. An accelerometer system comprising: an inertial platform defining areferenced plane, a spin axis, and a linear acceleration axis, whereinsaid spin axis is within said reference plane and said linearacceleration axis is perpendicular to said reference plane, saidinertial platform maintaining a minimized rotation in response to aplatform stabilizing controller signal; a first accelerometer defining afirst flex axis, said first accelerometer coupled to said inertialplatform a first distance from said spin axis, said first accelerometergenerating a first accelerometer signal in response to acceleration ofsaid first accelerometer; a second accelerometer defining a second flexaxis, said second accelerometer coupled to said inertial platform asecond distance from said spin axis, said second accelerometergenerating a second accelerometer signal in response to acceleration ofsaid second accelerometer; and a controller receiving said firstaccelerometer signal and said second accelerometer signal, saidcontroller generating a linear acceleration signal in response to a sumof said first accelerometer signal and said second accelerometer signal,said controller further generating said platform stabilizing controllersignal in response to said first acceleration signal and said secondacceleration signal.
 2. The system of claim 1 wherein said firstaccelerometer generates a first linearized digital output signal inresponse to acceleration of said first accelerometer, and said secondaccelerometer generates a second linearized digital output signal inresponse to acceleration of said second accelerometer.
 3. The system ofclaim 1, wherein said controller comprises a first compensatorcompensating for a non-linearity within said linear acceleration signaland generating a first digital word proportional to a linearacceleration in said reference plane.
 4. The system of claim 3, whereinsaid controller further generates an angular acceleration signal from afraction of a difference of said first accelerometer signal and saidsecond accelerometer signal.
 5. The system of claim 4, wherein saidcontroller further comprises a second compensator compensating for anon-linearity within said angular acceleration signal and generatingsecond digital word proportional to a rotational acceleration about saidspin axis.
 6. The system of claim 5, wherein said controller controls amissile system in response to said first digital word and said seconddigital word.
 7. The system of claim 1, wherein said first accelerometeris a first bridge accelerometer and said second accelerometer is asecond bridge accelerometer.
 8. The system as in claim 1, wherein saidfirst flex axis and said second flex axis are perpendicular to saidlinear acceleration axis.
 9. A method for operating a dual bridgeaccelerometer system defining a z spin axis comprising: generating afirst accelerometer signal from a first bridge accelerometer; generatinga second accelerometer signal from a second bridge accelerometer;controlling said first bridge accelerometer and said secondaccelerometer such that said first bridge accelerometer and said secondbridge accelerometer remain in an xz-plane; generating a first outputword from said first bridge accelerometer equivalent to a sum of a firstlinear acceleration and a first tangential acceleration acting on saidfirst bridge accelerometer; generating a second output word from saidsecond bridge accelerometer equivalent to a sum of said first linearacceleration and said first tangential acceleration acting on saidsecond bridge accelerometer; averaging said first output word and saidsecond output word; and generating a linear acceleration signal.
 10. Themethod of claim 9 further comprising compensating for non-linearitieswithin said linear acceleration signal.
 11. The method of claim 9further comprising generating a digital word proportional to an angularacceleration around a z-axis.
 12. The method of claim 11 furthercomprising activating an object control device in response to saiddigital word.
 13. The method of claim 9 further comprising averagingsaid first output word and a negative value of said second output wordand generating an angular acceleration signal.
 14. The method of claim13 further comprising compensating for non-linearities within saidangular acceleration signal.
 15. The method of claim 13 averaging saidfirst output word and a negative value of said second output wordfurther comprises generating a difference of amplitudes of said firstoutput word and said second output word.
 16. An accelerometer systemcomprising: an inertial platform defining a reference plane, a spinaxis, and a linear acceleration axis, wherein said spin axis is withinsaid reference plane and said linear acceleration axis is perpendicularto said reference plane, said inertial platform maintaining a minimizedrotation in response to a platform stabilizing controller signal; afirst accelerometer defining a first flex axis, said first accelerometercoupled to said inertial platform a first distance from said spin axis,said first accelerometer generating a first linearized digital outputsignal in response to acceleration of said first accelerometer; a secondaccelerometer defining a second flex axis, said second accelerometercoupled to said inertial platform a second distance from said spin axis,said second accelerometer generating a second linearized digital outputsignal in response to acceleration of said second accelerometer; and acontroller comprising a first compensator and a second compensator, saidcontroller receiving said first linearized digital output signal andsaid second linearized digital output signal, said controller generatinga linear acceleration signal in response to an average of said firstlinearized digital output signal and said second linearized digitaloutput signal, said first compensator compensating for a non-linearitywithin said linear acceleration signal and generating a first digitalword proportional to a linear acceleration along said linearacceleration axis, said controller further generating an angularacceleration signal from a difference of said first linearized digitaloutput signal and said second linearized digital output signal, saidsecond compensator compensating for a non-linearity within said angularacceleration signal and generating a second digital word proportional toan angular acceleration about said spin axis, said controller furthergenerating said platform stabilizing controller signal in response tosaid first linearized digital output signal and said second linearizeddigital output signal, and said controller controlling a missile systemin response to said first digital word and said second digital word. 17.The system of claim 16, wherein said first accelerometer is a firstbridge accelerometer and said second accelerometer is a second bridgeaccelerometer.
 18. The system of claim 16, wherein said controller is amissile computer.
 19. The system of claim 16, wherein said firstcompensator is a linear lookup table providing compensation informationto said controller.
 20. The system as in claim 16, wherein said firstflex axis and said second flex axis are perpendicular to said linearacceleration axis.